Diluting a diet with oat hulls of different particle size enhances gastrointestinal development and function of weanling pigs

Insoluble dietary fibers (IDF), especially in coarse form, are considered beneficial for gastrointestinal tract (GIT) development in weanling piglets. This study aimed to determine the effect of feeding diets with high IDF by including 15% oat hulls (OH), either finely or coarsely ground, on GIT development in weanling piglets. A total of 72 piglets (Hypor Libra × Hypor Maxter, 26 ± 0.6 d, 7.0 ± 1.2 kg bodyweight [BW]) were housed in three large pens (24 piglets/pen). Each pen was equipped with three electronic feeding stations and each station contained one of three experimental diets (n = 8 piglets/dietary treatment). The control (CON) diet consisted of finely ground highly digestible ingredients. For the OH diets, 15% finely ground (OH-f) or 15% coarsely ground OH (OH-c) were included at the expense of corn starch. A total of 12 randomly selected piglets/diet were euthanized on d13 post-wean for GIT measurements. Empty stomach weight was highest for OH-c, followed by OH-f, and CON (9.66, 8.78, and 7.32 g/kg BW, respectively; P < 0.001). Weights of gastric content (P = 0.028), cecum content (P = 0.032), empty colon (P = 0.027), and colon content (P = 0.024) were higher for OH-f and OH-c compared to CON. Piglets fed the OH-c diet had a higher pH gradient (0.93; P < 0.001) and smaller DM gradient (-2.3%-point; P = 0.025) between the proximal and distal area of the stomach compared to both CON (-0.12 and -9.4%-point, respectively) and OH-f (0.23 and -4.3%-point, respectively) caused by higher pH (P = 0.004) and DM (P < 0.001) in the proximal stomach. Total VFA concentrations were higher in OH than for CON in the stomach, cecum and colon especially for OH-c. Although not significant, the goblet cell counts and goblet cell area were numerically higher in both OH diets than in CON (+30% and +45%, respectively). In conclusion, diluting a nutrient-dense diet by inclusion of 15% OH in the immediate post-weaning period resulted in a more developed and functional GIT (i.e., increased goblet cell counts and area, increased organs weights and increased total VFA production), which was even more pronounced when the OH were in a coarse form.